Constant velocity universal joints to be used as, for example, means for transmitting a rotational force from an engine of an automobile to wheels at constant velocity are classified into such two types as a fixed type constant velocity universal joint and a plunging type constant velocity universal joint. The two types of constant velocity universal joints have a structure capable of transmitting rotational torque at constant velocity even when two shafts, namely, a drive shaft and a driven shaft are coupled to each other to form an operating angle.
Drive shafts for transmitting power from the engine of the automobile to driving wheels need to allow angular displacement and axial displacement along with changes in relative positional relationship between the engine and the wheels. Thus, the drive shafts each generally include a plunging type constant velocity universal joint on the engine side (inboard side), a fixed type constant velocity universal joint on the driving wheel side (outboard side), and an interconnecting shaft for coupling the two types of constant velocity universal joints to each other.
The fixed type constant velocity universal joint and the plunging type constant velocity universal joint each generally include an outer joint member having an inner peripheral surface including track grooves that are formed at a plurality of positions on the inner peripheral surface and extend in an axial direction, an inner joint member having an outer peripheral surface including track grooves that are formed at a plurality of positions on the outer peripheral surface and in pairs with the track grooves of the outer joint member, the track grooves of the inner joint member extending in the axial direction, and torque transmitting members interposed between the track grooves of the outer joint member and the track grooves of the inner joint member.
Examples of the fixed type constant velocity universal joint include a Rzeppa type constant velocity universal joint (BJ) and an undercut free type constant velocity universal joint (UJ) of a ball type including balls that are used as the torque transmitting members. Further, examples of the plunging type constant velocity universal joint include a double offset type constant velocity universal joint (DOJ) of a ball type including balls that are used as the torque transmitting members. Those constant velocity universal joints generally include six balls.